Dear katalin,
I want to find the reason of the phase transiton for AgF by calculating
the phonon dispersion curves. My intent is finding the soft mode at high
pressure.
>Which was the first grid, which you used to calculate the dispersion?
AgF is fcc strcture, c/a is 1, so the mesh was initially chosen as 4*4*4.
At 3GPa, after calculating the eight special points, i found only one of them
(0,0,1) has a negative mode. Then i did the calculation of the phonon
disperion curves with q2r.x, the frequences of TA near the gama point are
negtive. Near gama point, i just selected one q, whose TA is negtive, to
calculate the phonon, but the value of the TA is positive. I thought the q
mesh is small, so i chose 6*6*6 mesh.
> Does the 6x6x6 mesh include also the points you calculated for checking.
The 6*6*6 mesh dosen't include the above modes which has negtive values,
but i cannot find other ways to avoid the unexpected negtive values.
thank you for your advice.
best regards
Li Yan
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